No, Upper Moon 1 is not stronger than Muzan. Muzan Kibutsuji is the main antagonist in Demon Slayer and the progenitor of all demons. He possesses immense power and is considered the strongest demon in existence.
While Upper Moon 1, Kokushibo, is incredibly powerful and considered one of the strongest demons, he is still a subordinate to Muzan. Kokushibo's strength comes from his immense physical abilities, mastery of the Breath of the Sun, and his demon blood art. However, Muzan's power surpasses even Kokushibo's due to his unique abilities:
- Blood Demon Art: Muzan can manipulate his blood to create powerful attacks and regenerate from injuries.
- Immortality: Muzan is essentially immortal, making him extremely difficult to kill.
- Progenitor Power: As the progenitor of all demons, Muzan has a natural dominance over other demons, including Upper Moon 1.
Muzan ultimately defeated Kokushibo in their final confrontation, demonstrating his superior power.